1. Field of the Invention
The present invention relates to a novel configuration for power generation, coupling a so called humid air turbine cycle (HAT) to a partial oxidation scheme.
The configuration comprises the steps of partially oxidizing the fuel with oxygen or an oxygen-containing gas (GASIFICATION) to yield a gas stream containing combustible gas and steam, quenching said stream with water to cool and saturate the stream, removing sulphur compounds from the stream and burning the stream (fuel gas) in a special purpose gas turbine, making direct use of steam contents of the fuel gas.
The gas turbine is arranged in a humid air turbine (HAT) cycle meaning that sensible heat originating from the turbine cycle is transferred to an air saturator as hot water to humidify and saturate the air which is subsequently used in a combustor.
The sensible heat originating from GASIFICATION is transferred to the HAT-cycle via water saturation and heating of the fuel gas.
The main advantage of the present invention is to simplify the integration between the gas generating part and the HAT-cycle and thereby simplifying the design and operation of the plant and minimizing the necessary liaison between the involved technology suppliers.
A further advantage of the present invention is that it simplifies the technology development and manufacture of the combustion turbine set. With the present invention it is possible to utilize the same combustion turbine arrangement when used both as a stand-alone natural gas fired HAT-cycle and when integrated with a gasification plant.
These terms used herein shall have the following meaning:
______________________________________ GASIFICATION: Partial oxidation of a carbonaceous fuel with oxygen or an oxygen-containing gas to yield a gas stream containing combustible gas. GASIFICATION A plant including GASIFICATION and PLANT: down-stream processes to make the combustible gas from GASIFICATION suitable for burning in a combustion turbine. HAT-cycle: Humid air turbine cycle in principle as des- cribed in EP 0 150 990 B1. IGHAT: An integration of a GASIFICATION PLANT and a HAT-cycle. CC: A Combined Cycle unit consisting of a combustion turbine and a steam turbine cycle, the latter cycle receiving its heat from the exhaust heat of the combustion turbine. Carbonaceous As used herein means any carbon containing fuel: fuel such as coal, oil, bio-fuel and waste fuel. ______________________________________
2. Description of the Related Art
When utilizing a combustion turbine for power production the combustion turbine is often arranged in a so called combined cycle (CC) configuration comprising a combustion turbine and a steam turbine cycle, the combustion turbine having its air compressor installed on the same shaft as the expander turbine and being designed without intercoolers and the steam turbine cycle taking its heat from the hot exhaust gases from the combustion turbine.
Prior art in the field of integration of a GASIFICATION PLANT and a CC, commonly known as IGCC, includes a CC developed for firing rich fuels such as natural gas or distillates. When such a CC is fed with a lean (diluted) fuel from a GASIFICATION PLANT the air flow from the combustion turbine air compressor must be reduced in order to keep the correct combustion turbine inlet temperature. Such a decrease can be effectively accomplished in a CC if the air compressor has sufficient margin to its surge point.
EP 0 150 990 B1, Process for Producing Power, discloses an alternative method to the CC for recovering the chemical energy in a fuel to produce electric power utilizing a combustion turbine. The sensible heat in the combustion turbine exhaust gases and in the compressed air is utilized to saturate the compressed combustion air with water and to preheat the saturated air and the fuel prior to combustion. This method for producing power has thus eliminated the steam cycle and is commonly known as the Humid Air Turbine cycle or the HAT-cycle.
Integration of a GASIFICATION PLANT and a HAT-cycle, called IGHAT (Integration of Gasification and a Humid Air Turbine Cycle), has been studied for a number of years. A major work describing the state of the art of the IGHAT development is the report "A Comparison of Humid Air Turbine (HAT) Cycle and Combined-Cycle Power Plants" by Electric Power Research Institute in the US, dated March 1991 (IE-7300). The process development approach is based on the principle that all sensible heat available from GASIFICATION and from the HAT-cycle is utilized to produce hot water, which is used to humidify the compressed air in the HAT-cycle before it is fed as combustion air to the combustion turbine. This type of heat integration results in two disadvantages.
1. The GASIFICATION PLANT and the HAT-cycle are highly integrated and will demand strong commercial and technical liaison between two different entities, which in many cases could benefit from being commercially separated.
2. The degree of humidification of the compressed air flow and the size of the air flow differs widely between an independent HAT-cycle using natural gas as fuel and for a HAT-cycle integrated into an IGHAT plant. Therefore different mechanical changes have to be made to the combustion turbine set in order to make it operate efficiently in both applications. This very much increases the cost for the combustion turbine development and manufacture work.
U.S. Pat. No. 5,117,623, Operating Flexibility in IGCC stations, discloses a method for recovering the sensible heat from partial oxidation of a carbonaceous fuel with oxygen or an oxygen-containing gas (GASIFICATION) utilizing a water quench to cool and water saturate the combustible gas stream from said GASIFICATION, passing the stream through a heat exchanger in which the stream is further cooled by heat exchange with circulating water so that liquid water is condensed from the stream, expanding the stream by lowering its pressure and removing sulphur compounds from the stream before or after lowering its pressure, resaturating and heating the stream and then burning the stream in a combustion turbine to produce power, wherein it is the circulating water aforesaid which is used to provide the heat for resaturating the stream. The process further comprises the step of passing the quenched stream through a boiler to raise steam prior to passing the quenched stream through said heat exchanger for heating circulating water.
The above invention reveals a simple method to transfer the sensible heat from GASIFICATION to the CC utilizing water saturation of the sulphur cleaned gas and steam production. To make the heat transfer more efficient the process includes gas expansion in a gas expander producing power.
EP 0 259 114 B1, Clean Electric Power Generation, discloses a method for the production of electric power from a carbonaceous fuel which comprises partial oxidizing of the fuel with oxygen or an oxygen-containing gas (GASIFICATION) to yield a gas stream containing carbon monoxide and hydrogen (synthesis gas) at supra-atmospheric pressure, quenching the stream with water creating a water saturated stream, expanding the gas stream to produce power, and combusting the expanded stream with additional oxygen or an oxygen-containing gas to produce additional power, characterized in that, prior to expansion, the gas stream is subjected to a carbon monoxide shift reaction whereby at least some of the carbon monoxide therein is converted into carbon dioxide and hydrogen. The process also includes a sulphur removal step. The process further comprises the step of passing the quenched stream through a boiler to raise steam prior to passing the quenched stream to the carbon monoxide shift reactor.
The above disclosure describes a method to transfer the sensible heat from GASIFICATION to the CC utilizing water saturation of the sulphur cleaned gas and steam production. To make the heat transfer more efficient the process includes a carbon monoxide shift reaction and gas expansion in a gas expander to produce power.